This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section.
Band pass filters are used in a radio's front end to let through only wanted frequencies. A band pass filter in a base station radio is generally made from cavity resonators that are coupled together. Macro base station transmit filters require very high quality factor (e.g., Q) resonators with large power handling, which leads to large filters. To reduce the size of the filter, multiple modes per resonating cavity can be exploited. Also, most macro base station filter specifications require very sharp filter selectivity, therefore it is of major advantage to have multiple transmission zeros close to both sides of the passband.